Communication system



COMMUNICATION SYSTEM 2 Sheets-Sheet 1 Filed May 17, 1945 VOLTAGE SOURCE l l i F! G. I

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INDTCATOR VOLTAGE SOURCE INVENTOR. STANLEY N. VAN VOORHIS BY f M AMQAAM.

ATTORNEY P 1951 s. N. VAN voom-us 2,567,862

COMMUNICATION SYSTEM Filed May 1'7, 1945 2 Sheets-Sheet 2 to FIGZ to a a -5 4 e PIG L 4a-ss DELAY LINE l t I45 $144 n |32 t "I26 l M FIG'B 8+ v INVENTOR. us E? STANLEY N-VAN vooRHls 4-!- 4 1 BY lo '03,; Tl; M-"M Q/M' ATTORNEY Patented Sept. 11, 1951 Stanley N. Van Voorhis, Rochester, N.

. by mesne assignments, to the United signer,

Y., al-

Statcs of America as represented by the Seoretary of War Application May 17, 1945, Serial No. 594,258

7 Claims.

This invention relates to communication systems and more particularly to systems involving transmission of a plurality of signals each conveying its own intelligence.

In accordance with the present practice. it is often desired to transmit intelligence from a moving object such as a ship or airplane to another ship or plane, or to a stationary position such as a ground station. Quite often in these instances, it is desired to transmit additionalintelligence such as might be used for synchronization of devices located at the sending and receiving stations. K

Several attempts have been made to find a solution to this problem. The use of difierent methods of modulation for the two signals was tried. For example. the regular signal might be transmitted by amplitude modulation and the synchronizing signal transmitted by frequency modulation. This solution involved considerable additional equipment and was found unsatisfactory for air-borne use. Another method which was tried but found unsatisfactory was that of transmitting certain identifiable and separable signals as synchronizing signals. However, atmospheric disturbances as wellas man-made interference could and did adversely affect the synchronization.

An object of the present invention is, therefore. to provide a reliable data transmission system, and a more specific object is to provide asystem in which the synchronizing signal is transmitted in the form of a position-modulated pip which is demodulated by a video tracking circuit to reproduce the original synchronizing signal.

Another object of the invention is to provide a system which will transform mechanical motion to electrical signals which are transmitted.

.demodulated. and reconverted to mechanical motion.

A further object of this invention is to provide a system for transmitting a plurality of voltages and demodulating the transmitted signal to reproduce the original voltages.

A still further object of this invention is to provide a position modulating and demodulating system.

For a better understanding of the invention, together with other and further objects thereof. reference is had to the following description taken in connection with the accompanying drawings. in which:

Fig. 1 is a block diagram of the invention;

Fig. 2 shows several waveforms produced by components of the circuit represented in Fig. 1;

in u

Fig. 3 is a typical pip-generating circuit or position-modulating circuit such as might be used in this invention: and

Fig. 4 is a typical video-tracking circuit or position-demodulating circuit such as might be used in this invention.

Referringv now particularly to Fig. l of the drawings, there is shown a block diagram of the invention. A master synchronizing oscillator circuit II, which may be of a conventional design, drives a delay circuit l2, sucsh as a delay multivibrator, and a signal source ii. 'A typical delay multivibrator or pip-generating circuit is shown in Fig. 3 and will be described in greater detail hereinafter. Signal source I! may comprise any conventional system modulated by intelligence which is to be transmitted. The signal source I! drives a conventional transmitting circuit N which in turn feeds into an antenna It or other radiating device. The delay circuit 1! drives a pip-generating circuit it. The circuit It in turn drives a pip generator l1 and also drives the transmitter ll. The pip which drives the transmitter it will normally be of greater amplitude than subsequent pips which are applied to the transmitter II from sources other than generator It. A voltage source 2| or the voltage on lead 22 of voltage source 23 controls pip generator I! whose output drives a mixer 24 and a pip generator 25. The mixer 24 is any conventional mixer, usually a vacuum tube circuit. A voltage source 26 or the voltage on lead it of voltage source 23 controls pip generator 25 whose output drives the mixer 24., The first of the series of pip-generating circuits. i. e.. generator II, is freerunning. and may be of a conventional design.

Each of the other generators l2, l6. l1 and 25. which also'may be of'a conventional design, controls the starting time or operating action of .the generator or circuit following it. From the foregoing, it will be understood that a voltage source is provided for each of the generators or circuits ".13, ll, l6, I1. 24 and 25, to control the time of generation of the pip output or other output of that generator or circuit.

The output of pip generator 25 may be used to drive another pip generator which may drive another, and so on. There is no theoretical limit to the number of pip generators which may be so connected. It will be recognized that there is of course a practical limit.

The voltage source 28 comprises a motor I! or other driving means which rotates an antenna 33 or other desired device. Contact arms 36 and 35 of a sine-wound potentiometer 38 are physiplitude greater placement from another given point. A unidirectional voltage source 4| connects to the poten tiometer 36 at its minimum resistance points. Leads 22 and 3| connect the contact arms 34 and 35, respectively, to the pip generator H and pip generator 25.

An antenna 42 at the receiving station connects to a receiver 43. The receiver 43 drives a clipping circuit 44, or other pulse discriminating circuit, and a signal indicator 45. In genblocks 23. 5|, 1s, and uric. 1, are unused.

The lead 46 connecting clipper 44 to generator .54, will be used. In the general embodiment, the pip generator l6 becomes a. master reference source of pips.

A pip is herein taken to be a voltage pulse whose amplitude may vary from 5 to 50 volts or more, and whose duration may vary from 1 to 50 microseconds. The pips from the source It are regularly spaced and may occur at from 500 to 5000 per second. The numerical values here given are not to be taken as limitations of eral, the pulse discrimination is performed on the basis of pulse amplitude, and the clipping circuit 44 may be a biased diode or other circuit capable of passing only signals of an amthan a predetermined value. The signal indicator 45 may be a loudspeaker, earphones, cathode ray tube or other suitable indicating device. The lead 46 is not connected when the circuits within the dashed block 5| are used.

The clipper 44 drives a secondary synchronizer 62. Synchronizer 52 is similar to synchronizer ll, except that it is not free-runnin but is controlled. The synchronizer and a delay circuit 53 which is similar to delay circuit l2. The circuit 53 drives a pip generator 54, similar to generator H, which in turn drives a pip generator 55 and similar to generator 25 and a video-tracking circuit 56. The video-tracking circuit 56 is fully described in the discussion relating to Fi 4. The videotracking circuit 56 is also driven by the receiver 43 directly and by the receiver 43 through a delay circuit 6|. The delay circuit 6| is normally in the form of a delay line. A delay line may be defined as a transmission line or artificially simulated transmission line in which in- I telligence applied at one end does not appear instantly at the'other end, but appears there only after a finite time delay.

The tracking circuit 56 drives conventional amplifiers or other desired circuits 62. The generator 55 drives another tracking circuit 63 which is similar to the tracking circuit 56, also driven by the receiver 43. The tracking circuit 63 drives conventional amplifiers or other desired circuits 64. The circuits 62 and 64 drive conventional summing amplifiers 66 and 65. respectively, as indicated. A summing amplifier is one which gives an output that is a function of the difference in amplitude of the two signals applied thereto. A sine-wound potentiometer 1| driven by a motor 12 and energized by voltage source 13, also drives amplifiers 65 and 66. The amplifiers 65 and 66 drive a conventional circuit 14 which controls the speed and direction of rotation of the motor I2. The motor 12 drives a rotating indicator 15. Indicator I5 may comprise a servo apparatus, the coils of a magnetic deflection cathode ray tube, or other desired device.

Referring now to the operation of the system, it will be first described in its more general embodiment. The waveforms of Fig. 2 will be constantly referred to for simplicity of explanation in this discussion. In Fig. 2, the capital letter P denotes pip, and the subscript denotes the circuit from which the waveform is taken. In the general embodiment, all circuits within, and all 52 drives indicator 45 the invention. The time at which the pip is initiated by source l6 will be called to to. The pip output of source It is shown in Fig. 2. and denoted by P16. This pip goes to the transmitter H where it will be transmitted. This pip or another one formed simultaneously therewith actuates pip generator |l, which produces a pip P11 after a time interval determined by thecontrol voltage from the source 2|. The occurrence or position of this pip will vary about a time t1 between such limits as to and ta. N0 variation occurs during one cycle, i. e., between reference pips from source l6, but variation in the position of the pip Pr: occurs over a period of time including several reference pips P16. This positional variation is illustrated by Pr: (Fig. 2). It is thus seen that P11. Fig. 2, is position-modulated by the voltage from source 2|.

The pip from generator |'I goes to the mixer 24 and also actuates generator 25. The generator 25in turn produces a pip P25, Fig. 2, whose position in time varies about time t4 between limits such as t5 and to. The control voltage from source 26 controls the position of P25.- The output of generator 25 is fed to the mixer 24. Any number of voltage sources and generators may be added to this series in a manner similar to the connections shown herein. The outputs of the generators l1 and 25, and others which leads emanating from, or going into the dashed 15 might be added, are combined in mixer 24. The resulting output is shown in Fig. 2. as P24. This output P24, combined with the output P16, drives the transmitter |4 to produce an output P14, Fig. 2, which is fed to the antenna l5.

The transmitted energy is received by antenna 42 and sent through the receiver 43. The receiver output P43, Fig. 2, is identical to P14, Fig. 2. The output P43 divides, and a portion of it passes through the clipping circuit 44. Only the pip representing to appears in the output P, Fig. 2. The output P44 actuates generator 54 which produces an output pip P54, Fig. 2, which in turn drives tracker 56 and actuates generator 55 to produce output P55. The output P4: of the receiver 43 travels through two paths to the tracking circuits 56 and 63. One of the two paths contains the delay line 6|. The resulting input to tracker 56 is shown as P43-5s in Fig. 2. These two pips, one of which was delayed, together with the pip from generator 54, produces an output from tracker 56 having a waveform the same as the voltage which produced the modulation of the pips from receiver 43. This output voltage is used to control the pip from the generator 54 and also is fed to the amplifier 62. The voltage output of amplifier 62 will be the same as the voltage which was applied to generator I! from source 2|. A pip from generator 55 and pips from receiver 43 drive tracker 63 to reproduce the modulation of the pips from the receiver 43 in the same manner as was described above for generator 54 and tracker 56. The voltage output from amplifier 64 will aaaaaca this invention may be generator It by a like amount (750 microseconds). After the elapse of the required time (750 microseconds), the generator I5 starts the same sequence which was described above in detail.

The control-voltage sources 2I and 26 may be considered as replaced by voltages on leads 22 and El from source 23. The motor 32 which drives the antenna 33 also drives the sine-wound potentiometer 35. A unidirectional voltage from source M is applied across the potentiometer as shown. The two arms 30 and 35 will pick ofi voltages from the potentiometer 36 which vary sinusoidally and cosinusoidally with respect to the ground terminal of source assuming the direction of rotation to be as indicated. These sine and cosine voltages are then respectively applied to control the pip generators II and in the receiving system similar actions occur. The output of clipper circuit 33 drives a synchronizing circuit 52 which turns on the indicator 05 for a period of time (750 microseconds). During this period of time the signals originating in signal source I3 will appear at the indicator 05. Simultaneously, the synchronizer 52 also actuates delay circuit 53 which deiays the action of the generators 50 and 55 by the proper amount (750 microseconds). The outputs from the tracker circuits 50 and I53 will be sine and cosine voltages, respectively. These voltages are sent through amplifiers 52 and 60 and to summing amplifiers 55 and 65, respectively. The summing amplifiers 65 and 65 are also fed by sine and cosine voltages; respectively, from a sine-wound potentiometer II which is energized by a unidirectional voltage source 73, and is similar to potentiometer 35. The summing biasing capacitors amplifiers and 65 have outputs indicative of" the difference in amplitude of the two voltages being applied to each. The outputs of amplifiers 05 and 66 are fed to amplifier I I which controls the speed and direction of rotation of motor I2 in such a manner as to maintain the output of the amplifiers 65 and 65 unchanged. 'The motor drives the rotary indicator 75 as shown. It will be seen that the indicator I5 will follow in exact synchronism the movements of the antenna 33.

Referring now more particularly to Fig. 3, there is shown a type of conventional pip generator or delay circuit which may be used in this invention. It comprises triodes BI and 92 or other suitable tubes with plate load resistors 93 and 90. The resistance 94 is smaller than the resistance 93. The cathodes 95 and 96 have a common load resistor IOI. In series with resistor IOI is an inductance I02 and a resistance I03. A grid I04 of tube 92 is returned to B+ through resistor I05 and is connected by a capacitor I06 to plate III of tube 9|. A grid II2 of tube 9| is returned .to ground through a source of potential I I 3 which may be constant or variable depending upon the use which is being made of the circuit. 3+ and ground constitute the plus and minus terminals, respectively, of a power source, not shown. Waveform II 3 indicates the actuating pip which is coupled into the circuit by capacitor H5, and wave form the output pip.

Considering now the operation of the circuit. it will be noted that the grid I00 of tube 92 is returned to 3+ and, therefore, tube 92 wil be normally conducting. The cathodes 9 5 and will be at some potential above ground. The maximum value of voltage applied by the source H0 is such that the tube 0I will remain normally cut off. The pip (wave form III) is coupled through capacitors H5 and I00 tothe grid I00 of the tube 92. This pip will cause tube 92 to be cut oil. Tube 08 conducts less heavily than tube 92 because of the larger resistor 93 and the eiiect of the voltage II3, and as a result, the cathodes 95 and 95 will be at a lower potential than normally with respect to ground. Other things being constant, the value of this cathode voltage above ground is determined by the voltage source II3. After tube 32 is cut oil, the charge on condenser I00 changes and the grid I00 will start rising in potential toward 13+. The time required before tube 92 again conducts will depend, other things being constant, upon the cathode voltage. The pip shown in waveform I It will be formed by inductance I02 and resistance I03 when tube 92 again conducts. The time delay of this output pip after occurrence of the exciting pip will depend upon the voltage M3. Th voltage H3 thus serves to modulate the position in time of the output pip IIG. If voltage H3 is constant. the pip H5 will represent a constant delay.

Referring now more particularly to Fig. 4, there is shown a type of conventional video tracking circuit which may be used in this invention. The circuit illustrated in Fig. 4 is disclosed and claimed in the copending application of Edward F. MacNichol, Jr. Serial No. 534,310, filed May 5, 194.4. It comprises triodes I 2! and I22 or other suitable tubes with plate load resistors I23 and I20. The tubes I 2I and I22 are provided with cathode biasing resistors I25 and I26, cathode I3! and I32, and grid resistors I33 and I30. Resistors I20, I25 and I33, and capacitor I3! are connected together as shown. Resistor I23 connects to B a terminal negative with respect to ground. A third tube I35 has a plate load resistor I30, which connects to the positive terminal 3+, and a cathode biasing resistor MI and biasing capacitor I02. A resistor I 43 together with the resistor IM forms a voltage divider network between B and ground. The terminals designated as 3-, ground and 3+ constitute three terminals of a power source not shown. Resistor I26 and capacitor I32 of tube I22 are connected to the resistors HI and I43 as shown. The point between resistors I25 I I6 indicates and I24 is conected by a resistance IM to the grid the sending stations by a device such as shown in Fig. 3. The pip I55 is generated by a device at the receiving end such as shown in Fig. 3. It is desired that pip I55 be caused to remain fixed relative to pips I55 and I51. If this is done, then the voltage from source I I3 (Fig. 3) which causes pip I55 to be stationary with respect to pips I56 and I51 will be the same as the original modulating voltage at the sending station. It will be obvious to those skilled in the art that if the time relationship of the pips is as shown in Fig. 4, both tubes HI and I22 will conduct equally, and the charge on the capacitor I46 will remain unchanged. Therefore, the voltage at the plate I59 of tube I35 will remain unchanged.

To show the operations of this circuit, assume the pips I56 and I51 advance in time. It can then be seen that the tube I22 will conduct more than the tube I2I. In this case the capacitor I46 loses.

charge, and the grid I45 drops in potential, while the voltage at plate I59 rises. If the voltage at plate I'59 is fed back at the voltage from source II3 (Fig. 3) the pipe I55 will be made to occur sooner and thus again occur at a time which is between the two pips I56 and I51. It can also be shown that the reverse action will occur if pips I56 and I51 occur later in time. Therefore, it is seen that the voltage at plate I59 follows the voltage which caused position modulation at the sending end.

From all the foregoing, it will be seen that my improved communication system is particularly adaptable to meet the specific requirement, wherein certain signals, such as intelligence, are to be transmitted for a portion of a cycle, e. g., 750 out of each 1000 microseconds, and synchronizing voltages are to be transmitted during the remaining portion of the cycle. The synchronizing voltages are effective to synchroniz a rotating antenna such as 33, and a rotating in! dicator 15. At the receiving station, the intel-- ligence signals are heard over a loudspeaker, or in earphones, or are observed on the screen of a cathode ray tube, depending upon what type of equipment or device is used for the indicator l5.

While there has been described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention. For example, this apparatus will work equally well if all pip generators are activated by the master .synchronizer rather than by the preceding pip generator as described hereinbefore. Corresponding changes would be made in the receiving device wherein the pip generator would be activated by the secondary synchronizer. Other changes may be made as dictated by circumstances, within the purview of the invention.

What is claimed is:

1. A communication system comprising a transmitting means; first synchronizing means;

signal means associated with said first synchronizing means in such a manner as to bemade alternately operative and inoperative thereby, said signal means being adapted to modulate said transmitting means; first delay means having a distinguishable first pip output, said first delay means being adapted to be actuated by said first synchronizing means, said first delay means being further adapted to modulate said transmitting means; first driving means; first unidirectional voltage means; first potentiometer means energized bysaid first voltage means; first and second contact means moved on said first potentiometer means by said first driving means, said first and second contact'means being respectively disposedtoiproduce sine and cosine voltage variations; first generating means having a second pip output, said first generating means bein adapted to be actuated by said first pip output of said first delay means, said first generating means being further responsive to the voltage on one of said first and second contact means to control the time of generation of said second pip output; second generating means having a third pip output. said second generating means being adapted to be actuated by said second pip output of said'first generating means, said second generating means,

being further responsive to the voltage on the remaining of said first and second contact means to control the time of generation of said third pip output; mixing means associated with said second and third pip qutputs and said transmitting means in such amanner as to cause said transmitting means to be. modulated by said second and third pip outputs; receiving means; second delay means; pip-discriminating means associated with said receiving means and said second delay means to control starting time of said second delay means; indicator means controlled by said receiving means and said second delay means to reproduce the output of saidsignal means; third generating means having a fourth pip output, said third generating means being actuated by said second delay means; third delay means; first tracking means associated with said receiving means, said third delay means and said third generating means in such a manner as to track said second pip output of said first generating means; first amplifier means responsive to said first tracking means to provide a voltage output identical with the voltage on the one of said first and second contact means associated with said first generating means, fourth generating means havinga fifth pip output. said fourth generating means being adapted to be actuated by said fourth pip output; second tracking means asso: ciated with said receiving means, said third delay means and said fourth generating means in such a manner as to track said third pip output of said second generating means; second amplifier means responsive to said second tracking means to provide a voltageoutput identical with the voltage on the one of said first and second contact means associated with said second generating means; second driving means; second uni-- directional voltage means; second potentiometer means energized by said second voltage means; third and fourth contact means moved on said second potentiometer means by said second driving means, said third and fourth contact means being respectively disposed to produce sine and cosine voltage variations; third amplifier mean: controlled by said first amplifier means and the voltage on one of said third and fourth contacI means to produce an output proportional to the difference in magnitude of the voltages from said first amplifier means and said one contact means; fourth amplifier means associated with said second amplifier means and the remaining of said third and fourth contact means to produce an output proportional to the difference in magnitude of the voltages from said second amplifier means and said remaining contact means; and

fourth amplifier means to correlate the operation of said second driving means with the operation oi'said first driving means.

2. A communication system comprising a transmitting means; first synchronizing means; signal means associated with said first synchronizing means in such a manner as to be made alternately operative and inoperative thereby, said signal means being adapted to modulate said transmitting means; first delay means having a distinguishable first pip output, said first delay mean being adapted to be actuated by said first synchronizing means, said first delay mean being further adapted to modulate said transmitting means; first generating means having a'second pip output, said first generating means being adapted to be actuated by said first pip out put of said first delay means; first voltage means associated with said first generating means for controlling the time of generation of said second pip output; second generating means having a third pip output, said second generating means being adapted to be actuated by said second pip output of said first generating means; second voltage means associated with said second generating means for controlling the time of generation of said third pip output; mixing means associated with said second and third pip outputs and said transmitting means in such a manner as to cause said transmitting means to be modulated by said second and third pip outputs; receiving means; second delay means; pip discriminating means associated with said receiving means and said second delay means to control starting time of said second delay means; indicator means controlled by said receiving means and said second delay means to reproduce the output of said signal means; third generating means having a fourth pip output, said third generating means being actuated by said second delay means; third delay means; first tracking means associated with said receiving means, said third delay means and said third generating means in such a manner as to track said second pip output of said first generating means; first amplifier means responsive to said tracking means to provide a voltage output identical with the voltage of said first voltage means; fourth generating means having a fifth pip output, said fourth generating mean being adapted to be actuated by said fourth pip output; second tracking means associated with said receiving means, said third delay means and said fourth generating means in such a manner as to track said third pip output of said second generating means; and second amplifier means responsive to said second tracking means to provide a voltage output identical with the voltage of said second voltage means.

3. A communication system comprising a transmitting means; first generating means having a pip output, said first generating means being associated with said transmitting means in such a manner as to modulate said transmitting means; synchronizing means for controlling the starting time of said first generating means, said synchronizing means being adapted to modulate said transmitter with a distinguishable pip; variable voltage means associated with said first generating means to provide a time delay proportional to the instantaneous value of the voltage of said variable voltag mean between the time of generation of said pip output and said starting time; receiving means; second generating means having a pip output; pip discriminating means associated with said receiving '10 means and said second generating means to control the starting time oi said second generating means; delay means; video tracking means associated with said receiver, said delay means and said second generating means in such a manner as to track said pip output of said first generating means; and amplifier means responsive to said tracking means to provide a voltage output identical with the voltage of said variable voltage means.

4. A communication system comprising a transmitting means; a first plurality oi generating means having pip outputs, said first plurality of generating means being associated with said transmitting means in such a manner as to modulate said transmitting means; synchronizing mean for controlling the starting time 0! said plurality of generating means, said synchronizing means being adapted to modulate said transmitter with .a distinguishable pip; a pinrality or variable voltage means associated with said first plurality of generating mean to provide time delays in each of said plurality of generating means respectively proportional to the instantaneous value of each or the voltages of said plurality of variable voltage means between the respective time 01' generation of said pip outputs and the starting time of each o1 said plurality of generating means; receiving means; a second plurality of generating means having pip outputs; pip discriminating means associated with said receiving means and said second plurality of generating means to control the respective starting times of said second plurality of V generating means; delay means; a plurality of video tracking means associated with said receiver, said delay means and said second plurality of generating means in such a manner as to track said pip outputs of said first plurality of generating means; and a plurality oi amplifier means associated with said plurality of tracking means to provide voltage outputs respectively identical with the voltages of said plurality of variable voltage means.

5. A communication system comprising a transmitting means; first generating means having a pip output, said first generating means being' associated with said transmittingmeans in such a manner as to modulate said transmitting means; synchronizing means for controlling the starting time of said first generating means; variable voltage means associated with said first generating means to provide a time delay proportional to the instantaneous value or the voltage of said variable voltage means between the time of generation 01' said pip output and said starting time; receiving means; second generating means having a pip output; delay means; and video tracking means associated with said receiver, said delay means and said second generating means in such a manner as to track said pip output of said first generating means.

6. A communication system comprising a source of a series of reference pulses; a first plurality of sources of variable voltages; means responsive to said plurality of variable voltages for deriving a like plurality of series of pulses from said series of reference pulses, wherein a first oi said plurality of series of derived pulses is position modulated relative to said series of reference pulses in accordance with a first of said plurality of variable voltages, and in a like manner each of the other series of said plurality of derived pulses is position modulated relative to the preceding series of derived pulses in accordance with a respective one of said plurality of variable voltages; means for transmitting and means for receiving said series of reference pulses and said plurality of series of derived pulses; and means responsive to said received series of reference ,pulses and each of said plurality ofreceived series of derived pulses for means for delaying each of said received series producing a like plurality of voltages varying respectively in accordance with each of said first plurality of variable voitages.

7. A communication system comprising a source of a series of reference pulses; a source of of reference pulses for said given time interval;

and means responsive to said received series of intelligence signals; means for transmitting said reference pulses and means for transmitting said intelligence signals for a given time interval after each reference pulse; means for delaying each pulse of said series oi reference pulses for said given time interval; a plurality of sources of variable voltages; means responsive to said plurality of variable voltages for deriving a like plurality of series of pulses from said series of delayed reference pulses, wherein a first of said plurality of series of derived pulses is position modulated relative to said serie or delayed reference pulses in accordance with a first of said plurality ofvariable voltages, a second of said plurality of series of derived pulses is position modulated relative to said first series of derived pulses in accordance with a second of said plurality of variable voltages, and in a like manner each of delayed reference pulses and to each of said plurality of received series of derived pulses for producing a like plurality of voltages varying respectively in accordance with each of said flrstmentloned plurality of variable voltages.

STANLEY N. VAN VOORHIS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,267,827 Hubbard Dec. 30, 1941 2,321,971 Becker June 15, 1943 2,371,415 Tolson Mar. 13, 1945 2,377,902 Relson June 12, 1945 2,389,692 Scherwin Nov. 27, 1945 2,426,654 White Sept. 2, 1947 2,472,535 Jones June 7, 1949 

